Conventional radio frequency (RF) transceivers include either a circulator or a transmit/receive (T/R) switch to selectively couple an antenna port to either a transmit chain or a receive chain of the transceiver. Conceptually, the transmit/receive (T/R) switch is a single-pole double-throw (SPDT) switch that (i) couples a first radio frequency (RF) port (e.g., a TX port) to a common RF port (e.g., a TRX port) and isolates the common RF port from a second radio frequency (RF) port (e.g., an RX port) in a transmit mode, and (ii) couples the common RF port to the second radio frequency (RF) port and isolates the first RF port from the common RF port in a receive mode. In general, the first RF port is connected to a RF signal path of the transmit chain, the second RF port is connected to a RF signal path of the receive chain, and the common RF port is connected to an antenna. Conventional transmit/receive (T/R) switches utilize a symmetrical structure that provides the same impedance (e.g., Z0) on the TX port, the RX port, and the TRX port. The symmetrical structure can result in larger voltage swings at the transmitter (TX) port.
It would be desirable to implement an asymmetrical transmit/receive (T/R) switch with a 90 degrees impedance transformation section.